The proposed work is designed to investigate specific aspects of B cell differentiation in normal and abnormal conditions, to elucidate mechanisms of specific models of B and T cell activation and to define functional interactions between macrophages, T cells and B cells in the avian model. Cell separation techniques, chromosome markers and in vivo and in vitro culture methods are employed in these experiments. Specifically, experiments are designed to further define the possible existence of separate cell lineages for precursor B and precursor T cells in hematopoietic tissues of embryos and in the post-embryonic period, a concept supported by recently obtained data. Additional work is concerned with in vitro differentiation of B cell precursors to functional B cells and with developing the methodology for obtaining clean preparations of large populations of functional macrophages for subsequent investigations on the interaction of T cells and B cells with macrophages in specific models of T and B cell activation respectively.